The use of networks to interconnect various station facilities in a data communications system is well known and is widely practiced. Examples of ring-topology networks include the ISO 8802-5 (1989) Token Ring Network and the ANSI X3.139-1987 Fiber Distributed Data Interface (FDDI). A non-ring topology network which may be given as an example is the ETHERNET type network. Regardless of the particular topology, however, a network which interconnects various station facilities is designed and intended to carry a substantial amount of traffic. Indeed, far more traffic is carried over the ring-topology network than can effectively be handled by any one station. Consequently, efficiencies dictate that each station on the network be able to rapidly perform at least two functions. First, each station must be able to readily identify the data which is destined for facilities at that particular station. Second, they must then receive only that data. Additionally, for some ring-topology networks, it is necessary for the station to also strip from the network data which originated at the station.
Electronic components, commonly known as Content Addressable Memories (CAM), are typically used for the address sorting function which is required at a station to identify data that is properly addressed to facilities at the station. In its operation, a CAM reviews and examines each frame of data that is transmitted over the network and compares the destination address of this data with the addresses of facilities which are known to be present at the particular station. If the facility is at the station, the frame of data is recognized by the CAM and the frame is copied to the destination facility. Otherwise, the frame is not copied and, instead, continues on the network.
In order for the CAM to efficiently and correctly select data from the network, address information in the CAM must be initially and periodically updated. This updating function is normally accomplished by a processor which is tied into direct communication with the CAM through dedicated circuitry. This dedicated circuitry, however, is typically part of a printed circuit board at the electronic interface between station and network and it usually occupies a substantial amount of space on the printed circuit board. Indeed, this dedicated circuitry can occupy sixteen or more pins. In any event, use of space for a dedicated purpose has consequent costs which should be avoided if possible.
A preferable alternative to dedicated circuitry is the use of a shared communications path. This is particularly so in the data communications field where compactness is a prerequisite. Accordingly, the present invention has recognized that a direct dedicated data communications link between a processor which accumulates address information about station facilities on a network, and a CAM which uses this address information to control the copying of data destined for facilities at the station, is not required. Instead, as recognized by the present invention, a preexisting communications path at the station can be effectively used for the transmission of address information from a processor to the CAM.
In light of the above it is an object of the present invention to provide a system for receiving data from a network destined for addressed facilities at a station on the network which effectively updates a content addressable memory with address information concerning the facilities at the station. Another object of the present invention is to provide a system for receiving data from a network destined for addressed facilities at a station on the network which reduces system componentry by sharing a common communications path at the station for the accomplishment of diverse functions. Still another object of the present invention is to provide a system for receiving data from a network destined for addressed facilities at a station on the network which effectively uses the network with minimal intrusion to accomplish the task of updating a station content addressable memory. Yet another object of the present invention is to provide a system for receiving data from a network destined for addressed facilities at a station on the network which is easy to implement, simple to use and relatively cost effective.